A large class of antiproliferative agents includes antimetabolite compounds. A particular subclass of antimetabolites known as antifolates or antifols are antagonists of the vitamin folic acid. Typically, antifolates closely resemble the structure of folic acid and incorporate the characteristic p-benzoyl glutamate moiety of folic acid. The glutamate moiety of folic acid takes on a double negative charge at physiological pH. Therefore, this compound and its analogues have an active, energy-driven transport system to cross the cell membrane and exert a metabolic effect. On the other hand, a compound without the glutamate group may passively diffuse into a cell.
A valid target for an antifolate is the enzyme thymidylate synthase. Thymidylate synthase catalyzes the C-methylation of 2'-deoxyuridylate ("dUMP") to provide 2'-deoxythymidylate ("dTMP"). This one-carbon transfer reaction is critical to cell division. Thus, a number of folate analogues have been synthesized and studied for their ability to inhibit the enzyme thymidylate synthase. A prototypic, specific, tight-binding inhibitor of thymidylate synthase, 10-propargyl-5,8-dideazafolic acid (T. R. Jones et al., "A Potent Antitumsor Quinazoline Inhibitor of Thymidylate Synthetase: Synthesis, Biological Properties and Therapeutic Results in Mice," Eur. J. Cancer 17:11 (1981)), has shown activity against ovarian, liver and breast cancer, with, however, troublesome hepatic and renal toxicities (A. H. Calvert et al., "A Phase I Evaluation of the Quinazoline Antifolate Thymidylate Synthase Inhibitor, N10-Propargyl-5,8-Dideazafolic Acid, CB3717," J. Clin. Oncol. 4:1245 (1986)). By addressing two properties in this class of molecule (solubility and capability for intracellular polyglutamation), a superior second generation analogue (ICI D1694) was developed.
Several lipophilic thymidylate synthase inhibitors have been developed recently. (See, e.g., E. M. Berman et al., "Substituted Quinazolinones as Anticancer Agents," U.S. Pat. No. 4,857,530; T. R. Jones et al., "Antiproliferative Cyclic Compounds," Copending U.S. patent application Ser. No. 07/432,338, which is a continuation application of Ser. No. 071251,765 filed Sep. 30, 1988; M. D. varney et al., "Antiproliferative Substituted Naphthalene Compounds," U.S. patent application Ser. No. 07/583,970 filed Sep. 17, 1990; S. H. Reich et al., "Antiproliferative Substituted Tricyclic Compounds," U.S. patent application Ser. No. 07/587,666 filed Sep. 25, 1990; L. R. Hughes et al., "Anti-tumour Agents," European Patent Application No. 373891, filed Dec. 12, 1989; and T. R. Jones et al., "Antifolate Quinazolines," U.S. patent application Ser. No. 07/812,274 filed Dec. 20, 1991).